Impulse wrenches are known in the art for tightening threaded fasteners. Certain types of wrenches heretofore known have a rotating manifold with a large bore formed therein, and a rotating spindle having a set of spring-biased vanes mounted thereon. The bore inside the manifold is provided with a pair of diametrically opposed lands. During operation, the manifold rotates relative to the spindle so that the vanes sweep along the interior of the manifold bore. This sweeping action creates a pressure differential on opposing sides of the vanes. When the vanes contact the lands, the spindle and manifold are momentarily coupled together in a force transmitting relationship and a rotary impulse is transmitted to the spindle through the vanes, thereby affecting a turning movement of the spindle and the fastener to which it is engaged.
These types of wrenches require extremely tight tolerances when forming the bore inside the manifold to ensure the vanes can sweep properly along the bore interior. As a result of such tolerances requirements, the cost of manufacturing such wrenches is relatively high.
Other types of arrangements for delivering impulses to the spindle have also been provided in the art. U.S. Pat. No. 3,210,959 to Brown discloses an arrangement wherein the manifold carries a single-acting piston that slides in a reciprocating manner within a radial bore formed in the impulse manifold. The output spindle has an eccentric portion disposed adjacent the radial piston. During a fastener tightening operation, the manifold rotates relative to the spindle such that the piston engages the spindle once each rotation to deliver a rotary impulse to the spindle. An overflow chamber is communicated to a chamber defined in part by the radial piston via a restricted orifice. As the eccentric portion of the spindle contacts the piston, the piston is cammed radially outwardly and pressurized fluid is forced through the restricted orifice. As a result, the piston rides over the eccentric spindle portion and then a return spring forces the piston back towards the spindle. When the torsional resistance of the fastener reaches a selected maximum level, a sufficient amount of fluid is forced out through the restricted orifice during each rotation to enable the piston to ride over the eccentric spindle portion without delivering sufficient force to further tighten the fastener. The maximum level for the torsional resistance of the fastener can be adjusted by turning a screw to vary the restriction of the orifice.
U.S. Pat. No. 5,735,354 discloses a piston-type arrangement that uses a single double-acting piston, and in another embodiment a piston-type arrangement using a pair of diametrically opposed pistons.
The advantage of a piston-type arrangement is that the high manufacturing expenses associated with machining the manifold bores for the vane-type arrangements within close tolerances are avoided. However, neither of the radial piston arrangements disclosed in the patents mentioned above have a suitable mechanism for shutting off the flow of power to the tool. In the '959 patent, the maximum torque level is set by varying the restriction of the aforementioned orifice by tightening or loosening a screw. The wrench of the '959 patent itself, however, continues to run after the threshold torque level has been reached. Thus, a user must visually verify that the maximum torque level has been reached by watching to see if the fastener is continuing to be tightened. As a result, the user may have a tendency to keep running the wrench more than necessary during each operation to ensure that the fastener is tightened. It can be appreciated that in high usage applications, such as in automobile assembly plants, extra running of the wrench can quickly add up over time and cause unnecessary premature wear on the wrench components.
The '354 patent does not disclose any mechanism for shutting off the power to the wrench or for ensuring that the torque applied by the fastener does not exceed a predetermined level. However, the applicants of the present application are aware of a commercially available impulse mechanism (the mechanism includes the manifold and the spindle, not the entire wrench) available from Robert Bosch GmbH, the assignee of the '354 patent, that is similar to the double-acting piston arrangement disclosed in the '354 patent. The Bosch mechanism uses a deceleration-sensitive shut-off structure for stopping the flow of power to the wrench. Deceleration-sensitive shut-off structures are problematic because they often measure the torque applied to the fastener inaccurately. Specifically, deceleration-sensitive shut-off structures measure the rotational deceleration of the wrench components to determine the torque being applied to the fastener. This method of measuring torque is inaccurate when tightening fasteners and using fastener engaging tools (i.e., the sockets used for engaging threaded bolts) of varying weights because these weights will affect the overall deceleration of the wrench components, thus resulting in inconsistent measurements and inconsistent torque delivery between fasteners of varying weights. In addition, these deceleration-sensitive mechanisms must be periodically adjusted to ensure the proper torque is being delivered.
Thus, there exists a need for a piston-type wrench that has a shut-off structure that functions effectively and consistently to shut-off power to the wrench when a fastener has been tightened to a preset torque. To meet this need, the present invention provides an impulse wrench for use in conjunction with a fastener engaging tool and a power supply to selectively rotate threaded fasteners. The wrench comprises a housing and an impulse manifold rotatably mounted within the housing. The manifold has a spindle receiving space and an impulse piston receiving space. An impulse delivering piston is mounted inside the impulse piston receiving space for reciprocating movement and has an impulse delivering surface and a pressurizing surface. The piston and the piston receiving space are constructed and arranged such that the pressurizing surface and an outer end portion of the piston receiving space cooperate to define at least a portion of a high pressure chamber which is filled with a substantially incompressible fluid.
An output spindle is rotatably mounted within the spindle receiving space and has an impulse receiving portion positioned adjacent the impulse delivering surface of the impulse piston. The output spindle connects with the fastener engaging tool such that rotation of the spindle rotates the fastener engaging tool. A power-operated motor is operatively connected to the impulse manifold. The motor is constructed and arranged to rotate the manifold about the driving axis thereof using power from the power supply. An actuator is selectively movable between (a) an actuated position enabling the power supply to communicate power to the motor and (b) a non-actuated position preventing the power supply from communicating power to the motor.
The impulse receiving portion of the output spindle and the impulse delivering portion of the impulse piston are constructed and arranged with respect to one another such that, when the motor is connected with the power supply and the fastener engaging tool is connected with the spindle and engaged with a threaded fastener, movement of the actuator to the actuated position thereof communicates power from the power supply to the motor to cause the motor to rotate the manifold relative to the spindle, thereby momentarily engaging the impulse delivering surface of the impulse piston with the impulse receiving portion of the spindle so that (a) an impulse is delivered to the spindle to apply torque to the spindle which in turn transmits the torque to the fastener engaging tool and the fastener engaged therewith and (b) the impulse piston moves such that the pressurizing surface thereof increases the fluid pressure inside the high pressure chamber to a level which is related to the torsional resistance to tightening offered by the fastener. An adjustable pressure responsive shutoff structure is communicated with the high pressure chamber and is movable between (a) a power communicating position wherein the shut-off structure permits the power supply to communicate power to the motor and (b) a power shut-off position wherein the shut-off structure prevents the power supply from communicating power to the motor. The shut-off structure moves from the power communicating position thereof to the power shut-off position thereof in response to fluid pressure in the high pressure chamber reaching a shut-off initiating level that is related to a selected maximum amount of torsional resistance to which the fastener is to be tightened, thereby preventing power from being communicated from the power supply to the motor when the torsional resistance of the fastener has reached the selected maximum amount. This prevents power from being communicated from the power supply to the motor when the torsional resistance of the fastener has reached the maximum amount.
The shut-off structure is constructed and arranged such that the shut-off initiating level of the fluid pressure in the high pressure fluid chamber at which the shut-off structure moves to the power shut-off position can be adjusted, thereby allowing for selective control of the maximum torsional resistance for the fastener.
The use of a pressure-sensitive shut-off structure that responds to pressure created as a result of the piston engaging the engaging portion of the spindle provides a consistent and accurate measurement of fastener torque, which in turn provides a consistent and accurate shut-off of power to the motor. Specifically, the pressure created by the piston moving outwardly is directly related to the amount of torsional resistance offered by a fastener. An increase in torsional resistance of the fastener results in an increase of pressure in the high pressure chamber during each piston movement. The pressure created by the piston is not affected by the weight of the fastener or other such variable factors, as is the problem with measuring deceleration of wrench components. Thus, measuring the pressure ensures a direct and accurate measurement of the fastener's torsional resistance without the inconsistencies created by other indirect torque measuring methods, such as deceleration measurements.
It is to be understood that this aspect of the present invention is not limited to the single-acting piston arrangement disclosed herein and may be practiced with any of the arrangements shown in the aforementioned '354 patent, the entirety of which is hereby incorporated into the present application. However, its is preferred to practice the principles of the present invention using a single-acting piston arrangement because a single-acting piston takes up less volume than a double-acting piston, which in turn allows more oil or another substantially incompressible fluid to be used in the manifold. Because of this increased fluid capacity in a single-piston arrangement, a greater volume of fluid can be used and thus the fluid temperature will increase less rapidly during operation than in comparison to a lower volume of fluid. As a result, the fluid in the single-acting piston design will need to be changed less often. Further, this aspect of the invention may be practiced with power-operated motors other than the air-powered motor disclosed herein. The motor may be powered by pressurized liquid or by electricity. In the case of using pressurized liquid as the power supply, a valve mechanism would still be suitable. However, a switch would be used when an electric power supply is used. Further, the principles of the present invention may also be practiced with the axial piston arrangement shown in EP 0631851 to Robert Bosch GmbH, the entirety of which is incorporated into the present application by reference.
Another aspect of the present invention relates specifically to fluid powered wrenches that use a movable valve to shut-off power to the motor. These valves reciprocate between open and closed positions to allow and prevent the flow of fluid to the motor. However, most of these wrenches use a complicated mechanism for moving the valve to its closed position. In such mechanisms, the fluid pressure usually resists such movement of the valve and thus the mechanism must actively move the valve.
U.S. Pat. No. 5,082,066, discloses an arrangement wherein pressurized air flowing from the power supply biases the valve towards its closed position. The valve is maintained in its open position during normal operation, and then allowed to move to its closed position under the force of the pressurized air. This arrangement is advantageous because it obviates the need for the complicated mechanisms required to force the valve against the resistance of pressurized air used in some wrenches. The problem with the arrangement disclosed in the '066 patent is that movement of the valve therein to its closed position is affected by a declaration-sensitive arrangement for measuring fastener torque. As discussed above, declaration-sensitive mechanisms may be inaccurate and inconsistent. As a result, the timing of the valve's movement to its closed position for power shut-off will also be inaccurate and inconsistent.
Thus, there exists a need for an impulse wrench in which the need for complicated mechanisms that move a valve against the resistance of pressurized fluid is obviated and also which is provided with an improved mechanism for measuring fastener torque. To meet this need, another aspect of the present invention provides an impulse wrench for use in conjunction with a fastener engaging tool and a supply of pressurized fluid to selectively rotate threaded fasteners. The wrench comprises a housing and an impulse transmitting mechanism mounted in the housing. The mechanism comprises a driven component, an output spindle, and surfaces defining a high pressure chamber filled with a substantially incompressible fluid. The output spindle is mounted for rotation with respect to the housing and connectable with the fastener engaging tool such that rotation of the spindle rotates the fastener engaging tool. A fluid-driven motor is operatively connected to the driven component. The motor is constructed and arranged to rotate the driven component using pressurized fluid from the supply. The driven component is rotatable with respect to the housing and the output spindle such that rotation of the driven component rotates the spindle to affect a fastener tightening operation wherein the threaded fastener is tightened in such a manner that its torsional resistance to tightening increases throughout the operation. The impulse mechanism is constructed and arranged such that the pressure of the fluid in the chamber increases to a level that is related to the torsional resistance offered by the fastener increases during the fastener tightening operation.
An adjustable pressure responsive shut-off structure is communicated with the high pressure chamber. The shut-off structure has a shut-off valve that moves between (a) a power communicating position wherein the shut-off valve permits the pressurized fluid to flow from the supply thereof to the motor and (b) a power shut-off position wherein the shut-off valve prevents the pressurized fluid from flowing from the supply thereof to the motor. The shut-off valve is positioned between the motor and the supply of pressurized fluid such that the pressurized fluid flows against the valve so as to apply a biasing force that urges the valve towards the power shut-off position thereof. The shut-off structure maintains the shut-off valve in the power communicating position thereof while the pressure of the fluid in the high pressure chamber is below a selected shut-off initiating level that is related to a selected maximum amount of torsional resistance to which the fastener is to be tightened and thereafter allows the valve to move to the power shut-off position thereof under the biasing force applied by the pressurized fluid flowing from the supply thereof in response to the pressure of the fluid in the high pressure chamber reaching the shut-off initiating level, thereby preventing the pressurized fluid from being communicated from the supply thereof to the motor when the torsional resistance of the fastener has reached the selected maximum amount.
The shut-off structure is constructed and arranged such that the shut-off initiating level of the fluid pressure in the high pressure fluid chamber at which the shut-off structure moves to the power shut-off position can be adjusted, thereby allowing for control of the maximum torsional resistance for the fastener.
This aspect of the present invention is not limited to the disclosed piston-type impulse mechanism. Instead, this aspect of the invention may be practiced with clutch-type mechanisms, such as that shown in U.S. Pat. No. 4,635,731, or with the vane-type mechanisms discussed above, such as those shown in U.S. Pat. Nos. 5,080,181 and 5,217,079, the entirety of each of these patents being incorporated into the present application by reference. Also, the principles of this aspect of the invention may be practiced with the axial piston arrangement shown in EP 0631851 to Robert Bosch GmbH, the entirety of which is incorporated into the present application.